Selective solvent refining process and solvent recovery



F. c. MccoY ETAL 2,935,468

4 Sheets-Sheet 1 sELEcTrvE soLvENT REFINING PRocEss AND soLvENT RECOVERY Filed April 1e, 195e May 3, 1960 May 3, 1960 F. c. McCoy ETAL SELECTIVE SOLVENT REFINING PROCESS AND SOLVENT RECOVERY Filed April 16, 1958 4 Sheets-Sheet 2 May 3, 1960 F C. MCCOY Em. 2,935,468

SELECTIVE SOLVENT REFINING PROCESS AND SOLVENT RECOVERY May 3, 1960 F, C. McCOY ET AL SELECTIVE SOLVENT REFINING PROCESS AND SOLVENT RECOVERY Filed April 16, 1958 4 Sheets-Sheet 4 2,935,468 SELECTIVE soLvENT REFINING PROCESS AND soLvENr RECOVERY vFrederic C. McCoy, Beacon, N.Y., and MarshallrR.

McClure, Jr., Port Arthur, Robert A. Woodle, Nederland, `and Robert L.`Murphey, Groves, Tex., assignors to Texaco Inc., a corporation of Delaware Application April 16, 1958, Serial No. 728,806 9 Claims. (Cl. 208-321) This invention relates to the recovery of selective solvent from admixture with hydrocarbons and to a petro- -leum treating process involving a solvent reiining operation. In accordance with one embodiment this invention `relates to `an improved petroleum solvent :refining operation. .In accordance with another embodiment this 1nvention is directed to an improved method of recovering selective solvent from admixture with hydrocarbons, particularly hydrocarbons havingV a similar bo-iling point.

In a solvent reiining operation as usually practiced in 4the `petroleum rening industry aliquid selective solvent sulting ratlinate and extract by distillation. In `someinstances, howeventhe boiling point of atportion'` of the petroleum fraction undergoing fractionation by solvent extraction closely approximates the yboiling point ofthe particular selective solvent-employed. In these instances the vseparation of the selective solvent-from.therainate rand/or -extract by fractional distillation is diflicult or uneconomical. More particularly, it has beenrproposed to eifec't a fractionationof petroleum naphtha fraction and the like into aromatic and relatively less aromatic por# tions by solvent extraction employing liquid furfural as `thes'elective solvent.- Unfortunately, however, the boiling point ofL furfural (about 324 F.) is Within therange of the boiling points of the constituents separated with the result that substantially complete separation of the furfural from the resulting railinate, and extract by fractional distillation is difficult.

Accordingly, it is an object of this inventiontoprovide `an improved method for the solvent refining of petroleum fractions containing components having a boiling point approaching that of the selective solvent` employed.

Another object of this invention is to provide an improved method for the recovery or separation of a selective solventfrom substantially co-boiling hydrocarbons.

v Another object of this invention is to provide van im-V proved method for the recoveryoffurfural `from a rafinate mix orv from an extract mix produced in afurfural ,solvent rening operationof apetroleum traction, such as a heavy vnaphtha or a fraction in the kerosene boil-ing range, particularlya petroleum fraction having an initial boiling point (i.B.P.) below about 625 F.

Still another objectoff this invention is to provide an improved method, involving washing or a subsequent ture with hydrocarbons. I

How these and other objects of this invention are accomplished will become apparent in the light of the ac- Subsequently in the petroleum reiining United States Patent O `solventextraction operation, for therecovery of anor- -mally liquid polar organic selective solvent from admix y 2,935,468 Patented May 3, 1960 Fig. 2 schematically illustrates one embodiment ofthe practicerof this invention in a solvent refining operation directed tothe recovery of selective solvent, and wherein lFig. 3 schematically illustrates another embodiment of ice `the practice of this invention directed to the recovery of a selective solvent, and wherein Fig. 4 schematically illustrates another embodiment of Ythe practice of this invention directed lto the recoveryiof selective solvent employed in a solvent reiining operation.

In accordance-with our invention we have discovered that a normally liquid selective solvent, such as a normally liquid polar organic selective solvent for aromatic hydrocarbons, is advantageously separated from single liquid phase admixture with hydrocarbons by contacting said admixture with an aqueous hydrotropic solution which exhibits a preferential solubility for said selective solvent and which it at least partially immiscible with the admire ture undergoing treatment. There is recovered from the aforesaid contacting operation a resulting aqueous hydrotropic `solutionnowcolntaining selective solvent dissolved therein. v

The aqueous hydrotropic solution employed in the practice of this invention comprises an aqueous solution v of a hydrotropethat is, a material such asa water soluble salt,fe.g., salt of an organic acid, which when dissolved in wwaterincreases the solvent power of water for polar organicmaterials `normally insoluble or 4only sparingly Vsoluble in water. Any hydrotrope whichwhen dissolved in water yields an `aqueous hydrotropic solution having an increasedor preferential solubility for normal liquid polar organic compounds, is suitable for use in the practice of this invention. Typical suitable hydrotropes inv"clude the water soluble alkali metal arylsulfonates, yparticularly the water soluble, relatively low molecular weight .sodium aiylsulfonates and sodium alkarylsulfonates such'assodium benzenesulfonate,,potassium benrzenesulfonate soditun Ytoluenesulfonate, potassium. tolujenesulfonate, and the sodium xylenesulfonates and the potassiumxylenesulfonates Generally an arylsulfonate,

`which includes alkarylsulfonates,.e.g.', C1-C10 alkyl-substituted benzenesulfonates, containing less than v16 carbon atoms per molecule is suitable. Other suitable hydrotropes linclude the water soluble salts of aliphatic monocarboxylic acids and the alkali metal alkylsulfonats `derived from the corresponding alkanes, such as propane,

butane, pentane, hexane, heptane and the like.

Other known hydrotropes or hydrotropic agents, and mixtures thereof, are suitably employed in the practice ofrthis invention. it is preferred in the practice of this Vinvention to employ concentrated aqueous hydrotropic solutions, such as aqueous solutions wherein the concentration of the hydrotrope is in the range 1070% by .sene fraction or light lubricating oil, for the removal of aromatic hydrocarbons therefrom, a charge oil is introduced via line li into liquid-liquid solvent-refining zone 12 wherein it isbrought into direct countercurrent contact Vwith a liquid selective solvent, furfural, preferably water-saturated furfural, which is introduced into the upper portion of solvent refining `Zone 12 via line `14. Additional fresh furfural, as required, is addedto solvent rening zone 12jfrom a convenient source, not shown, via line 15 to line 145. Within solvent refining zone 12 `the charge ,oil is brought into intimate contact with the liquid selective "solvent, water-saturated furfural. The solvent refining zone12 may be operated under isothermal conditions or vat a temperature gradiengcne en d of the refining zone having a temperature diterent from the other end of the solvent rening zone. The ratio of selective solvent to charge oil introduced into solvent rening zone 12 will vary depending upon the characteristics of the charge stock and the extent of rening desired. Usually a solvent to charge oil volume ratio in the range .5 to 10.0 is employed.

There is recovered from the upper portion of solvent refining zone 12 via line 16 a liquid ranate mix. The rainate mix comprises the less aromatic hydrocarbons containing furfural dissolved therein. There is recovered from the other end of solvent refining zone 12 via line 18 a liquid extract mix. The extract mix comprises liquid selective solvent, furfural, containing the more aromatic hydrocarbons selectively extracted from the charge oil dissolved therein. The rainate mix is introduced via line 16 into the lower end of raffinate mix stripper 19 wherein it is subjected to direct countercurrent liquid-liquid contact with a concentrated aqueous hydrotropic solution, such as a 40% by weight solution Yof sodium xylenesulfonate, which is introduced into the tropic solution which is introduced into the upper endV charge oil, said rafnate being substantially free of the selective solvent, furfural.

There is recovered from the lower end of raftinate mix stripper 19 via line 26 the aqueous hydrotropic solution now containing furfural dissolved therein. Similarly, there is recovered from the lower end of extract mix stripper 21 via line 28 another stream of aqueous hydrotropic solution containing the selective solvent, furfural, dissolved therein.

Extract mix stripper 21 and rainate mix stripper 19 are operated at a suitable temperature, such as a temperature in the range 70-220? F., more or less, depending upon the temperature conditions desired therein. The furfural-rich aqueous hydrotropic solution recovered from strippers 19 and 21 via lines 26 and 28, respective- 1y, are admixed in line 28 and introduced into hydrotrope concentrator 29 wherein the furfural is distilled overhead as Ia furfural-water azeotrope or constant boiling mixture (C.B.M.) via line 30. The furfural-water azeotrope is condensed by condenser 31 and the resulting condensate introduced via line 32 into decanter or separator 34 wherein it separates into a lower furfural or furtural-rich phase and a supernatant water or waterrich phase. The furfural-rich phase comprises furfural saturated with water and the supernatant water-rich phase comprises water saturated with furfural.

The furfural-rich phase is recovered from decanter 34 via line 14 for reintroduction into solvent refining zone 12 to effect solvent rening of additional charge oil. The furfural-saturated water phase is removed from decanter 34 and introduced via line 35 as reflux into the upper portion of hydrotrope concentrator 29. Desirably hydrotrope concentrator 29 is operated under conditions such that substantially no steam injection -is required. This is accomplished by withdrawing a bottoms fraction containing the substantially furfural-free concentrated hydrotropic -solution via line 36 and introducing the same The vapor vgenerated within reboiler 38 is introduced via line 40 into the lower portion of hydrotrope concentrator 29. The resulting hot concentrated, furfuralfree aqueous hydrotropic solution is recovered from reboiler 38 via line 41 and introduced, after suitable cooling, if desired, by means not shown, via lines 20 and 22 into strippers 19 and 21, respectively, for the recovery of furfural from the raiinate mix and extract mix issuing from the solvent refining zone. Make-up water, if desired or if required, mayA be introduced into the system from a suitable source, not shown, via lines 42 and 36 into reboiler 38.

In laccordance with another embodiment of the practice .of this invention the relatively furfural-lean aqueous hydrotropic solution issuing from the lower end of raffinate mix stripper 19 via line 26 may be employed, in whole or in part, to extract additional furfural from the extract mix in extract mix stripper 21 by introduction thereinto via lines 26, 44 and 22.

Accordingly, in the manner described hereinabove with respect to Fig. 1, the practice of our invention is applied to the recovery of furfural from an extract mix and a ratnate mix derived from a furfural solvent refining operation wherein an aqueous hydrotropic solution is employed to separate furfural from hydrocarbons present in said mixes.

Referring now to Fig. 2 of the drawing there is schematically illustrated another embodiment of the practice of this invention directed to the recovery of furfural from an extract mix issuing from a furfural solvent rening zone, such as solvent refining zone 12 of Fig. l, and the recovery of the furfural from the resulting fu'rfural-rich aqueous hydrotropic solution. Although the particular embodiment of the practice of this invention is illustrated in Fig. 2 with respect to the recovery of selective solvent, furfural, from extract mix, this embodiment of applicants invention is also applicable to the recovery of selective solvent from a rafnate mix issuing from a solvent rening zone, such as solvent retining zone 12 of Fig. 1.

As illustrated in Fig. 2 extract mix, such as furtural extract mix derived from solvent refining zone 12 via line 18 of Fig. 1, is introduced via line 51 into extract mix stripper 52 wherein it is brought into direct liquid-liquid countercurrent contact with an aqueous hydrotropic solution, such as a concentrated aqueous solution of sodium xylene sulfonate. The aqueous hydrotropic solution is introduced into the upper end of extract mix stripper 52 via line 54. There is recovered from one end of extract mix stripper S2 via line 55 extract now substantially free of furfural and comprising substantially only more aromatic hydrocarbons. There is recovered from the other end of extract stripper 52 via line 56 a furfuralrich aqueous hydrotropic solution which is introduced via this same line into hydrotrope concentrator 58. Hydrotrope concentrator 58 is supplied with a suitable heating element 59 through which ows a suitable regulated heating vHuid, such as steam. The amount of steam ilowing through heating element 59 is regulated by ow controller 60 in accordance with the temperature and/ or ow of vapors issuing from concentrator 58 via line 61.

The vapors from concentrator 58 via line 61 are introduced into condenser 62 wherein they are condensed and from which the resulting condensate ows via line 64 into decanter 65 wherein the condensate separates into a water-saturated furfural phase which is recovered via line 66 and a furfural-saturated water phase which is recovered via 'line 68. The furfural-saturated water phase is reintroduced into concentrator 58 via lines 68 and 56. The hydrotrope concentration of the aqueous solution within concentrator 58'as well as the liquid level of the solution therein is regulated and controlled by the use of water introduced into concentrator 58 via lines 67 and 56. The oW of this make-up water into concentrator 58 controlled by liquid level controller 69.

` drotropic solution introduced thereinto vial line 56 is con- ,.'centrated by the removal of furfural and water there- Afrom as a constant boiling mixturein the vapors issuing overhead via line 61.` There is recoveredV from concent trator 58 via line 70 a `concentrated hydrotropic solution, `now relatively lean with respect to or substantially free of furfural. The flow of substantially furfural-free concentrated hydrotropic solution from concentrator 58 via line V70.is regulated by flow control valve 71 operatively connected to concentration controller 72 which in turn is operatively connectedto concentrator 58.

The resultingV substantially furfural-free or partially :stripped aqueous hydrotropic solution issuing from contrator 58 via line 70 is introduced into the upper portion of hydrotropic solution-stripper 74 wherein it` isl subjected to direct liquid-liquid countercurrent contact with a suitable liquid hydrocarbon, suchtas charge oil from which the extract mix inline 51 may be` suitably derived, `as illustrated in Fig. l. The charge oil or other suitable hydrocarbon or petroleum fraction is introduced into Vhydrotropic solutionstripper 74 via line 75 to strip any residual urfural present in the aqueousfhydrotropicsolution introduced into stripper `74 viarline 70. .Accordingly there-issues from the upper portion of stripper'7.4 Via line '76 a charge oil now containing furfural dissolved there- `as'feed to a `suitable solvent refining operation, as illus- L`trated in'Fig. lof the drawings. Also, there is recmlercdV from the `lower-end of st ripper74vialine 54 jan aqueous Vhydrotropic'solution Anow substantiallyfreeof furfural. This furfuralstripped aqueous hydrotropic solution issufing from stripper 74 lvia line 54 is employed for .thelextraction' ofjfurfural from the extractmmix withinjextract fmix stripper-52. Y

"Referring now to Fig. v3 of-the -drawingfwhichmsche- :matically illustrates another embodiment'of the .practice of this invention and wherein the same reference numerals .have been employed to. designate similar apparatus'gand elements AVas. .found .in Eig. 2 .of the drawings, extract,mix lis introduced via line 51 into extract mix stripper 52 `wherein it is brought into direct liquid-liquid countercurirent contactiwith agpartially stripped aqueous hydrotropic :solution introduced y,into the upper portion of stripper 52 'yiayline 54. There is recovered from the upper 4portion fof stripper 5.2 appartially stripped extract mix via line 55. nalso there is recovered from the lower end of stripper `:52 vialine 56 a furfural-rch' aqueous `hydrotropic solu- .tion which is introduced into hydrotrope concentrator 58 fw-herein it Aisc'oncentrated by the applicationof heat .there- "to byl means of heating elementf59 which is controlledily operated for'the `ilow-ofa,suitable-heating.fluid-there- 4:throughby means oiilow controller 60j whichis operative- ,Ely connected with the'temperature and/criloworvapors emanating from concentrator 58 via linerl. `'lfhese vapors in line 61 larecondensed Yin condenser 62' andthe :resulting condensate introduced yialine. 64 into decante'r" `65 wherein they separate into a'water-saturated furffural `Vphase which is removed via line '66 and afurfural-satur- .ated water phase which is removed via line '63 for reintroiduction into concentrator' vialline 56. MMalce-upwater i 'hydrotropic solution issuing from concentrator -58 via line ly furfural-free extract lvia line 4v84.` vThere :is ,recovered Yfrom the lower end ofA stripper81 via line-85 `furfurz-il- :rich water which is introduced intothe upper endofwa- .ter stripper 86 wherein it is subjected to directliquidliquid countercurrent contact with a liquid petroleumiraction, such as a charge oil from which theextract mix was derived, introduced into the lower end of Waterstripper 86 via line 88. There is recovered fromthevupperendof water stripper 86 via line `89 charge oil now containing furfural dissolved therein, the furfural dissolved Ying-the charge oil recovered from stripper 86 via line 89 .being the furfural originally present in the partially stripped extract -mix introduced via line 55v into extract mix stripper 31. Also there is recovered -from the lower end` of water stripper via line 82 water now vsubstantially free lof furfural. This water is then introduced -via line 8 2'into the upper end of extract mixstripper 81 to eifectrremoval of furfural from the partially stripped extract mix there- 1n.

Referring now to Fig. 4 of the drawing which schematically'illustrates another embodiment of the practice of this invention as applied to the recovery of furfural from an aqueous hydrotropic solution employed for the re- -covery of a selective solvent, extract mix containing furfural dissolved therein is introduced via line 90 into extract mix stripper 91. Within stripper 911 the extract mix is subjected to direct liquid-liquid countercurrent contact with an aqueous hydrotropic solution for the recovery of the selective solvent therefrom. The aqueous -hydrotropic solution is introduced into the upper end of .stripper 91 via line 92. There is recovered from the upper end of stripper 91 via line 94 a substantially furfuralfree extract. There is also recovered from the lower end of Vstripper 91 via line 95 a relatively furfural-rich aqueous hydrotropic solution which is then introduced into q theteupper end of hydrotrope stripper 96. Within hydrowtrope stripper 96 the furfural-rich aqueous hydrotropic solution is subjected to direct liquid-liquid oountercurrent contactwith a relatively low boiling or read-ily separable, as by Afractional distillation, hydrocarbon or hydrocarbon fraction` introduced into the lower end of hydrotrope Vstripper 96 via line 97.

As a result of the above-indicated operations there is recovered from the lower end of hydrotrope stripper 96 via line 92 an aqueous hydrotropic solution substantially free of furfural. There is recovered overhead from hydrotrope stripper 96 via line 98 furfural dissolved in the relatively low boiling or readily separable hydrocarbon. The low boiling hydrocarbon containing funfural is `introduced via line 98 into fractionator 99 wherein the relatively low boiling hydrocarbon is removed overhead via line 100, condensed in condenser 101 and the resulting condensate supplied via line 102 into flow splitter 104 wherein a portion of the resulting condensed hydrocarbon is returned via line 105 as rellux to fractionator 99. Another portion of the `condensed low boiling hydrocarbon is returned via lines 106 and 97 to hydrotrope :'54 is `regulated by ilow control valve 71V operatively` con .i

,nected to concentration controller 72. v

The partially furfural stripped extract mix issuing overhead fromV stripperSZ via line 55.isintroducedinto-.iinal extract mix stripper 81 wherein it is` subjected to direct stripper 96. lThe bottoms issuing from the lower end of fractionator 99 via line 108 are introduced into reboiler 1 09 which is supplied with heating element 110 `supplied with suitable heating fluid. The vapors generated within reboiler 109 are returned to fractionator 99 via line 1121 and the remaining bottoms fraction comprising furfural substantially free of the low boiling hydrocar-bon is removed via line 112. In this embodiment of the practice of applicants invention a low boiling hydrocarbon, such as a hydrocarbon or hydrocarbon fraction readily separable by distillation from the selective solvent associated therewith, is employed in lieu of distillation to eiect removal of furfural from the furfural-rich aqueons `hydrotropic solution. Desirably the low boiling hydrocarbon or hydrocarbon fraction employed is an aro- .matie hydrocarbon, such as benzene, or a hydrocarbon fraction which is readily miscible with the selective solvent ,(zuffural) employed.

'vention Various petroleum refinery stocks, the proper- 2,985,488 v 7 Y The following is exemplary of the practice of this in- TABLE `I ties of which are set forth in accompanying TableA I, were Tests o" Charge oils subjected to furfural solvent refining under varying o on- You 80 Pale 100 Pale Bydmb ditiorns. 'l'he resulting extract mixes and rainate mixes 5 11e 011 derived from the solvent refining operations were then subjected to direct ooun-tercurrent liquid-liquid contact Refractive Index at 70C 1. 4892 1. 4915 1. 4620 with a concentrated aqueous hydrotropic solution, viz. I 22'6 22'3 30'9 a 40% by weight aqueous solution of sodium xyleneo 83 8 110.7 13.15 sulfonate to remove residual selective solvent, furfural, 1'0 ggo g: ggg ggg 2 from the raflinate mix and the extract mix. Following Pour. 1j` -60 -35 75 the foregoing operations there were recovered substantially furfural-free ratlnates and extracts. The test data 560 592 42o observed during the foregoing solvent refining operations gg ggg g together with the properties of the resulting recovered 15 724 722 56o raiinates and extracts are set forth in accompanying Cracked 754 620 Tables H IH and IV l Kiuematic viscosity, cs.

TABLE II Tests on furfural refined 80 pale oil Processing Conditions:

Solvent Dosage percent 125 219 338 Rainate Out et--Tempe Product..... Ext. Reit. Ext. Raft. Ext. Refi.

Product Yield, Vol. Percent 33. 1 66. 9 28. 9 71. 1 27. 0 73. 0 Product Tests:

RI 70 C 1. 5259 1.4700 1. 5331 1.4704 1. 5363 1.4708 Gravity, API 26. 9 26. 5 26. 9 Viscosity- SUS/100 F 85. 3 83. 3 83. 9 SUS/150 F 48. 1 47. 6 47. 8 SUS/210 F 37. 1 36. 8 36.8 Pour, F -45 -50 -50 Aromatics, Percentl 23.3 24. 6 23.9

Y 1 By silice gel adsorption.

` TABLE III Tests on furfural refined 100 pale oil Processing Conditions:

Solvent Dosage, Percent 117 150 205 Refunate Outlet-Temperature,

F 201 200 171 Extract Outlet-Temperature,

Product Ext. Rail. Ext. Raft. Ext. Ran.

Product Yield, Vol. Percent 33. 3 66. 7 28. 2 71. 8 22. 4 77. 6 Product Tests:

RI at 70 O 1. 5240 1.4752 1. 5337 1. 4748 1. 5465 1.4758 Gravity, API 25. 1 25. o 25. 1 Vscosity- SUS/100 F 105. 7 105. 5 107. 9

SUS/150 F 52.3 3 52. Q

SUS/210 F 38. 3 38.3 38.4 Pour, F -eo -eo -o Aromatics, Percent l 29. 9 2 30. 0

1 By silica gel adsorption.

TABLE IV Tests 0n furfural refined hydraulic oil Processing Conditions:

Solvent Dosage. Percent 163. 2 244. 3 263.8 Raiiinato Outlet-Temperature,

Extract Outlet-Temperature.

Product Ext. Raft. Ext. R211 Ext. Ba.

Product Yield, Vol. Percent 40. 8 59. 2 34. 9 65. 1 30. 5 69. 5 Product Tests: Y

RI at 70 O 1. 4840 1.4474 1. 4920 1. 4464 1. 4957 1. 4472 Gravity, APT 35.0 35. 4 84. 9 Viscosity- Kinemetic/l00 F 3. 53 3. 50 3. 44 Kinematicll5o F 2. 06 2. 05 2. 03 Kinematic/210 F 1. 30 1. 30 l. 29 Pour, F -75 -50 -15 Aromatics, Percent l 28.1 29. 0 30.2

l By silica gel adsorption.

v"i9 Extract .derived Yfrom :the Lforegoing 4'indicated .furfural :solvent refining operations `were..countercurrently Vlcontacted .with `a `40% by weight .aqueous solution of .Sodium xylenesulfonate, at a temperature of about .150 vF. .and yemploying a varying hydrotropic solution dosage inthe range 1D0-300% byvolume. 'Ilhe furfural extract mixes employed contained a major amount lby volume, about 80%, furfural.` 'Ilhere was recovered from these operations .an extract having a furfural content .of less than about 0.03% byvweight, even less than 0.01% by Weight. It was observed that by employing a hydrotropic solution to extract mix dosage greater than 215% vole, basis extract mix, a washed extract having less than 0.03% by weight furfural was obtained. 'Ilhe resulting Afat, `furfural-rich aqueous hydrotropic solutions were vseparated into furfural and aqueous hy- 'drotropc-solutionby fractional distillation. For example, a furfural-rich aqueous hydrotropic solution cornprising 19-20% furfural after having been subjected to fractional distillation yielded an aqueous hydrotropic solution containing in the range S28-36.3% by weight solids and a substantially insigniiicant amount of furfural, in the range 0.l-0.8% by weight.

Likewise, with respect to the solvent extraction of raffinate mixes wherein the selective solvent, furfural, comprises only a minor portion thereof it was observed that substantially the same dosage, about 225% by volume basis raliinate mix, was required in order to reduce the furfural content of the rainate to a substantially insignificant value, about 0.03% by weight. In these tests which were also carried out at a temperature of about 150 F. on a laboratory eight stage box counterflow unit employing 40% by weight aqueous solution of sodium xylenesulfonate as the aqueous hydrotropic solution the raffinate mix undergoing treatment contained approximately furfural.

During the foregoing tests it was observed that theV recovered aqueous hydrotropic solution was more eiffective than freshly prepared hydrotropic solution in removing furfural from admixture with the accompanying hydrocarbons. The data setting forth the superiority of recovered or used aqueous hydrotropic solutions over fresh aqueous hydrotropic solutions for the recovery of selective solvent, furfural, is set forth in accompanying Table V.

TABLE V Comparison between recovered and fresh aqueous hydrotrope-batch extractions [Charge: 80% {mural-40% 80 gale o]il extract. Dosage: 500% basis c arge.

Furfural Content Washed Extract, Wt. n Percent Extraction No.

liresh Solvent Recovered Solvent Nth .0999.57 geen As indicated hereinabove, the practice of this invention is useful for the separation of a normally liquid polar organic selective solvent from substantially coboiling hydrocarbons. Moreover, the practice of this invention is particularly useful in a solvent refining operation wherein a relatively high boiling selective solvent, such as furfural, as opposed .to vnormally gaseous sulfur` dioxide, is employed to solvent renne a relatively light or low boiling petroleum fraction, such as a petroleum ofA `ratnate' mixes and extract mixes derived from the furfural `solvent refining of petroleum fractions whichhave an `initial `boiling point of 500 F. or lower. By conventional methods the recovery of furfural from mixes derived from such charge stocks to yield a furfural-free .extract and/ or a furfural-free extract has been very ditiicult or substantially impossible. Y

Although considerable emphasis in this disclosure has been placed upon the applicability of the subject invention with respect to the use of urfural as the selective solvent and for the recovery of furfural, it is mentioned that, as disclosed herein, this invention is applicable for ,the recovery of any polar'organic selective solvent possessing a relatively high boiling point, especially a boiling pointapproximating the boiling point of components making up a petroleum fraction undergoing solvent rctining. More particularly, the practice of this invention is also suitable for use in a solvent refining operation employing a phenol, nitrobenzene, dimethylformarnide, or lBCt'-dichloroethylether and other relatively highv boiling selective solvents.

As will be apparent to those skilled in the art many modifications, substitutions and alterations in the practice of this invention as disclosed hereinabove are possible without departing from the spirit or scope thereof.

We claim:

1. A solvent retining process for the solvent refining of a liquid petroleum fraction having an initial boiling point below 625 F. which comprises contacting said petroleum fraction with liquid furfural to yield a liquid ratiinate mix containing furfural dissolved in the raffinate and an extract mix containing extract dissolved in the furfural, contacting said ratiinate mix in a liquid-liquid contacting operation with a concentrated aqueous solution of sodium xylenesulfonate to extract furfural from saidv raiinate mix, contacting said extract mix with the concentrated aqueous solution of sodium `xylenesulfonate to extract furfural from said extract mix and subjecting the resulting `aqueous hydrotropic solutions containing furfural dissolved therein to fractionation to remove furfural therefrom.

2. A method in accordance with claim l wherein the resulting aqueous hydrotropic solutions after removal of furfural therefrom are recycled to contact additional rainate mix and additional extract mix for the removal of furfural therefrom,

3.7A solvent relining process for the solvent refining of a liquid petroleum fraction having an initial boiling point below 625 F. which comprises contacting said petroleum fraction lwith liquid furfural to yield a liquid raffinate mix containing urfural dissolved inthe raflinate and an extract mix containing extract dissolved in the furfural, contacting said raffinate mix in a liquid-liquid contacting operation with a concentrated aqueous solution 'of sodium xylenesulfonate to extractfurfural from said ratiinate'mix, contacting said extract mix with the concentrated aqueous solution of sodium xylenesulfonate to extract furfural lfrom said extract mix and recovering furfural from the resulting aqueous hydrotropic solutions.

4.A A method in accordance with claim l wherein said petroleum fraction is a light lubricating oil.

5. A method in accordance with claim 1 wherein said' petroleum fraction is a heavy petroleum naphtha,

6. A method in accordance with claim l wherein after the removal of furfural from the aqueous hydro-. tropic solution by fractional distillation the resultingaqueous hydrotropic solution is contacted with fresh feed petroleum fraction to remove residual furfural therefrom.. 7. A method in accordance with claim l wherein said' petroleum fraction is in the kerosene boiling range.

8. A method of solvent reiining a liquid petroleum.A fraction having an initial boiling point less than 625 F. which comprises contacting said petroleum fraction with liquid furfural to yield a raffinate mix comprising g ratnate containing furfural dissolved therein and an` aromatic extract mix comprising furfural and extract dissolved therein, contacting said raffinate mix in a liquid- 4liquid contacting operation with an aqueous solution of antalkali metal arylsulfonate, said aqueous solution being immiscible with said rainate mix and said extract mix, to remove said furfural therefrom and employing the resulting aqueous solution, now containing furfural dissolved therein, to remove additional selective solvent from said extract mix. t

9. A method of solvent refining a liquid petroleum fraction having an initial boiling point less than 625 F. which comprises contacting said petroleum fraction with liquid furfural to yield a rainate mix comprising, raffinate containing furfural dissolved therein and an aromatic extract mix comprising furfural and extract dissolved therein, contacting said rainate mix in a liquid- 12 liquid contacting operation with an aqueous solution of sodium xylenesulfonate, said aqueous solution being immiscible with said rafnate mix and said extract mix, to Vrei'n'ove said furfural therefrom and employing the resulting aqueous solution, now containing furfural dissolved therein, to remove additional selective solvent from said extract mix. l

y References Cited in the le of this patent UNITED STATES PATENTS 2,210,541 Tijmstra v Aug. 6, 1940 2,567,228 Morrell et al .,Sept'. 11, 1951 2,612,468 Morrell et al. Sept. 30, 1952 2,654,792 Gilmore Oct. 6, 1953 2,706,707 Morrell et al. Apr. 19, 1955 2,745,790

Manley May 15, 1956 

1. A SOLVENT REFINING PROCESS FOR THE SOLVENT REFINING OF A LIQUID PETROLEUM FRACTION HAVING AN INITIAL BOILING POINT BELOW 625* F. WHICH COMPRISES CONTACTING SAID PETROLEUM FRACTION WITH LIQUID FURFURAL TO YIELD A LIQUID REFFINATE MIX CONTAINING FURFURAL DISSOLVED IN THE RAFFINATE AND AN EXTRACT MIX CONTAINING EXTRACT DISSOLVED IN THE FURFURAL, CONTACTING SAID RAFFINATE MIX IN A LIQUID-LIQUID CONTACTING OPERATION WITH A CONCENTRATED AQUEOUS SOLUTION OF SODIUM XYLENESULFONATE TO EXTRACT FURFURAL FROM SAID RAFFINATE MIX, CONTACTING SAID EXTRACT MIX WITH THE CONCENTRATED AQUEOUS SOLUTION OF SODIUM XYLENESULFONATE TO EXTRACT FURFURAL FROM SAID EXTRACT MIX AND SUBJECTING THE RESULTING AQUEOUS HYDROTROPIC SOLUTIONS CONTAINING FURFURAL DISSOLVED THEREIN TO FRACTIONATION TO REMOVE FURFURAL THEREFROM. 